1. Field of the Invention
The present invention relates to a delay line of the ceiling and ring type or of the ceiling and bar type for a travelling wave tube.
2. Description of the Prior Art
These two types of lines are now well known in the prior art. It is known in particular that these lines may propagate several modes: a principal mode and several parasite modes.
To ensure stability of the travelling wave tubes using these lines it is necessary:
on the one hand, to suppress the propagation of the parasite modes; PA1 on the other hand, for the principal mode, to avoid parasite oscillations which are troublesome, whether the tube operates as an amplifier or as an oscillator. PA1 for the parasite modes, on some rings is deposited a metal layer or a layer of an alloy such as Kanthal, (registered trademark), formed of aluminium, iron . . . PA1 for the principal mode, one or more cuts are made in the delay line and each line portion is connected to power loads provided with a cooling system; moreover, a deposit, of Kanthal for example, is made on some of the feet supporting the rings so as to "mask" by distributed losses of a few decibels the standing wave ratio or ROS due to these cuts. PA1 the metal or alloy layers covering some rings are efficient but generate high frequency losses in the principal mode, and so reduce the gain and the efficiency of the tube; PA1 and especially, the use of loads external to the tube requires the provision of transitions between the delay line and coaxial lines, coaxial windows, cooling systems for the power loads . . . . All these elements are costly and space-wasting: moreover, the passage of coaxial lines through the winding of the solenoid, which provides focusing of the electron beam along the axis of the tube, creates breakages of the solenoid which generate disturbances in the focusing of the beam.
In the prior art, the stability of travelling wave tubes comprising a ceiling and ring line is provided in the following way:
The problems which arise from these techniques used in the prior art and which our invention proposes resolving are the following:
Similar problems arise for practically all tubes comprising ceiling and bar lines, where substantially the same techniques are used to ensure stability.
The object of the present invention is to resolve the above-mentioned problems and in particular to suppress the loads external to the tubes.